CA1180856A

CA1180856A - Titanium clad steel plate

Info

Publication number: CA1180856A
Application number: CA000397542A
Authority: CA
Inventors: Fumihide Ueda
Original assignee: Asahi Kasei Kogyo KK
Current assignee: Asahi Kasei Corp
Priority date: 1981-03-05
Filing date: 1982-03-03
Publication date: 1985-01-15
Also published as: EP0060083B1; EP0060083A1; US4612259A; DE3263845D1

Abstract

ABSTRACT OF THE DISCLOSURE:
A titanium clad steel plate, wherein a cladding metal layer consisting of at least one layer of titanium or a titanium alloy is bonded, as one body, with a base metal layer consisting of at least one layer of carbon steel or low-alloy steel, through said cladding metal layer's and said base metal layer's bonding to an inter mediate layer of a metal selected from niobium, a niobium alloy, tantalum and a tantalum alloy, and a method of manufacturing the same which is useful as a structural material.

Description

1 The present invention realtes to a titanium clad steel plate haviny an excellent bond strenath and excellent bending ability even after hot processing during its manufacturing process or even after heat treatment after manufacturing process, and also to a method of manufacturing the same.
More particularly, the present invention relates ~o a titanium clad steel plate, wherein a cladding metal layer consisting of at least one layer of titanium or a titanium alloy is bonded, as one body, with a base metal ].ayer consisting of at least one layer of carbon steel or low alloy steel, through said cladding metal layer's and said base metal layer's bonding to an intermediate layer of a metal selected from niobium, a niobium alloy, tantalum and a tantalum alloy, and also relates to a method of manufacturin~ the said titanium clad skeel plate which is useful as a structural material.
A titanium clad steel plate is a clad steel plate of which base metal is steel and of which cladding metal is titanium or its alloy having excellent corrosion resistance and heat resistance, and is u-tilized in many applications.
As manufacturing methods of titanium clad steel plate, the roll bonding proce.ss, the diffusion l bonding process and others are recently being studied in addition to the conventional explosive bonding process. However, titanium clad steel plates manufactured by these new processes have problems. In the roll bonding process, brittle intermetallic compounds are formed during hot rolling and thereby a satisfactory bond strength can not be obtained. In the diffusion bonding process, the use of a base metal of which chemical component is modified or the use of an intermediate metal is proposed, however, any proposed method is not industrially adopted, except for trial manufacturing of small scale because problems similar to those of the roll bonding process still remain to be solved.
Accordingly, only titanium clad steel plate manufactured by the explosive bonding process is extensive-ly used as materials for chemical equipments.
However; titanium clad steel plate of this explosive bonding process also has problems. For instance, titanium plate being commercially manufactured and marketed has a width of only about 2.5 m or below and the plate of a larger width is not available. Also, when the base metal is a thin plate, due to strain caused by explosive bonding or reduction in elongation of the base met~l, titanium clad st~el plate having an area sufficiently large to respond to market needs is not available yet.
For improving the above situation, methods are belng tried which can obtain wider and/or longer ~v~s~

1 titanium clad steel plate hy hot-rolling the titanium clad steel plate. No such method, however, is industrial-ly used yet.
For example, Japanese Patent Publication No.
432/1969 discloses a method for obtaining explosive bonded and hot-rolled clad steel plate of excellent bond strength by hot-rolling, at about 475 to 900C, the titanium clad steel plate which has a brittle intermetallic compounds region and a direct titanium-to-steel bonding region.
However, the above method was found to be an incomplete one, after conducting a proving test.
Namely, the rolling temperature of this method is in a lower range compared with that of normal steel plate;
therefore/ work hardening of the base metal is remarkably high, its elongation in tension test does noc meet the specified value, and its workability in bonding is remarkably reduced. The application of a heat treatment at 540C or above ~or improviny the above characteristics of the base metal results in large reduction in bond strength between titanium and steel and, in many cases, leads to a shear strength below 14 kg/mm which is a minimum value in many titanium clad steel plate specifica-tions. The characteristics of the base metal could not be improved by heat treatment below 540~C.
The above reduction in bond strength is caused by the fact that, in the heat treatment process, mutual diffusion occurs between the cladding titanium and the 35~
1 base steel and thereby hard and brittle intermetallic compounds are ~ormed.
For improviny these defects, there is proposed a method in which an intermediate metal is interposed between titanium and steel in order to prevent mutual diffusion between titanium and steel.
As manufacturing methods of this multilayered titanium clad steel plate in which an intermediate metal is interposed, there are, in addition to the above-mentioned diffusion bonding process, other processes such as the roll ~onding, the physical vapor deposition and the electric plating, In view of reduc-tion in bond strength during hot rolling, multilayered titanium clad steel plate is most preferably manufactured by the explosive bonding process.
The thickness of this intermediate metallic layer should be made to an allowable rninimum level.
A thick intermediate layer will possibly cause new inconveniences in the case of the clad steel plate .~ requiring a welding operation. Also, since the inter-mediate metallic layer is generally made of noble metal or a rare metal or a such metal alloy, the clad steel plate in which an intermediate metal is interposed has an industrial meaning only when its intermediate metal is used in a quantity as small as possible.
The thic3~ness of the intermediate metal layer is sufficient in several millimicrons to several tens of millimicrons, from the standpoint of safe prevention ~ a~
l of mutual diffusion However, achievement of the aboYe thickness of the intermediate metallic la~er is difficult in the normal explosive bonding process. ~hen an inter-media-te metal of l mm thickness is used, rolling to one tenth to one hundredth thick becomes necessary. This necessitates that the thickness of a clad steel plate before hot rolling is lO to lO0 times thick that of the clad steel plate after hot rolling, and manufacture of such a clad steel plate can not be conducted industri-ally.
In order to improve such defects, the inventor had found out a very useful method as described in the previously applied ~apanese Patent Application Kokai (Laid-open3 No. 53888/1981.
In the method, firstly an intermediate metal such as nickel, molybdenum, platinum, gold or silver, all of which effectively prevent mutual diffusion, is explosive bonded to steel then this clad steel formed is rolled by hot rolling or the like to a minimum thickness allowed to the intermediate metal, and subsequently this e~plosive bonded and rolled clad steel plate is interposed between a cladding material and a base steel plate, and they (three layers) are explosive bonded according to the known explosive bonding process and further rolled, and thus a clad steel plate having a thin intermediate metal layer is obtained.
E~periments conduc-ted after filing of the above 1 patent application revealed that, when the method of the above patent application is applied to titanium clad steel, exceptionally, its ~ond strength after hot rolling is still low and the bond strenyth is further reduced by subsequent heat treatment.
Tha-t is to say, it became clear that the ahove intermediate metal such as nickel, molybdenum, platinum, ~old or silver has excellent bond strength to base steel even after hot rolling but has insufficient bond strength to cladding titanium after hot rolling.
In proving tests, explosive bonded and hot rolled clad steel plate (Ti/Ni/steel/steel) had a bond strength of less than 10 kg/mm2 as shear strength after rolling and did not meet 14 kg/mmZ mostly specified for titanium clad steel plates. Meanwhile, the titanium clad steel of the present invention showed a shear strength of over 25 kg/mm2, even after hot rolling during manufacturing process or even after heat treatment at above 540C after manufacturing process, and the titanium clad steel plate of the present invention was confirmed to possess an excellent bond strength.
The present inventor conducted various investi gations and experiments to improve these defects of titanium clad steel plate, and as its result, the present Z5 invention has been achieved.
This invention relates to titanium clad steel plate of at least three layers ~hich contains, between titanium and steel, at least one layer of an 1 intermediate metal containiny any one of tantalurn, a -tantalum alloy, niobium and a niobium alloy.
The titanium material used in this invention is commercially pure titanium (at least about 99.4%
titanium by weight) or titanium alloy plate containing at least 73.05~ by weight of titanium such as Ti-5Pd or the like, and is often referred to as titanium plate in this invention. The steel material used in this inven-tion is SS material, S~ material, SM material and SUS
material all specified in Japanese Industriai Standards (JIS), and carbon steel or low-alloy steel similar to the above materials, and the like.
Hereinafter, the titanium clad steel of the present invention is explained in detail referring to the accompanying drawings.
Figures 1 to 3 are the drawings illustrating embodiments of the present invention. In the drawings, numbers indicate the following materials, and capital alphabets indicate raw materials and small alpha~ets indicate materials a~ter processing.
1: Titanium plate

2: Intermediate metal

3: Steel plate

4: Supplemental intermediate layer

5: Three-layered clad plate

6: Two-layered clad plate

7: Four-layered clad plate

8: Five-layered clad plate 35~

1 Figure 1, (a) to (f) are drawings correspondiny to a manufacturing method of Claim 13 of the present invention~ In Figure 1, (a), 1-A is titanium plate, 2-A
an intermediate metal and 3-A steel pla-te. The inter-mediate metal 2-A must be a metal which has excellent malleability and ductility and does not form brittle intermetallic compounds at each interface plate l-A
and the steel plate 3-A. Researches revealed that the most suitable intermediate metals are commercially pure niobium, niobiwn alloys such as Nb-Zr and Nb-Ti, commercially pure tantalum, and tantalum alloys such as Ta-Nb and Ta-Ti.
The titanium plate l-A, the intermediate metal 2-A and the steel plate 3-A are bonded by the known method into a three-layered clad steel plate shown in Figure 1, (b)o This bonding is conducted preferably by the known explosive bonding process shown in many li-teratures such as USP 3137937, but can also be made by other methods such as the known di~fusion bonding process and the known roll bonding process as disclosed in INCRA
Research Report of Jwly 1976.
The explosive bonding process has two methods.
The one is a method in which firstly the steel plate 3-A and the intermediate metal 2-A are explosive bonded and then the titani~n plate l-A is explosive bonded on the surface of the intermediate metal 2-A. The other is a method i.n which three layers are explosive bonded 1 simultaneously. In the former method, surface rougheniny ocurrs on the surface of the intermediate metal 2-A
in the first explosive bonding. ~lso, niobium or tantalum is susceptible to oxidation at its surface because of its activation, and, ~or the remo~al of the surface oxide film, surface polishing becomes necessary, which causes the loss of the valuable material. On the other hand, in the latter method, the interposing of the intermediate metal 2-A between the titanium plate l-A and the steel plate 3-A and the explosive bonding of these three layers are carried out simulta-neously. Accordingly, the intermediate metal, even if it is an active metal, is not contacted with air, therefore is not oxidized and there is no n~ed of polishing.
Moreover, there is no surface rouyhening and no material loss.
This three-layered clad steel plate is hot rolled into a thin three-layered clad steel plate 5-a consisting of three layers l-a, 2-a and 3-a shown in ~0 Figure 1, (c).
The amount of thickness reduction by this hot rolling ~difference of plate thicknesses before and after rolling, amount of plate thickness decreased due to rolling~ varies depending upon rolling conditions such as rolling temperature and rolling mill capacity.
In existing facilities, the maximum amount of reduction will bP the one in which plate thickness is reduced to about one hundredth. The minimum amount of g _ ~ 3~ ~ ~

l reduction can be O mm of the diffusion bonding process.
In the present invention, the amount of reduction is not particularly specified.
The thin, three-layered titanium clad steel plate thus obtained was confirmed to have an excellent bond strength and excellent bending ability.
Further/ this thin, three layered titanium clad steel plate 5 a is interposed, as an intermediate metal, between cladding tit~nium l-s and base steel plate 3-B, as shown in Figure 1, (d), and these three layers are bonded by the use of a known bondiny process such as the explosive bonding process, the diffusion bonding process or the roll bonding process. Namely, the titanium plate l-a of the thin, three-layered titanium clad steel plate 5-a is bonded with the cladding titanium l-B, and the steel plate 3-a of the clad steel plate 5-a is bonded with the base steel 3-B.
The abo-ve bonding is also done either in the two step method (khe thin~ three-layered clad steel 2Q plate 5-a is bonded to the base steel 3-B and then the cladding titanium 1 B is bonded thereon) or in the one step method (simultaneous bonding of three layers).
The latter method is more effective. Figure l, (e) illustrates the bonded clad steel plate 8-A.
This clad steel plate 8-A is rolled into a slad steel plate 8-a having a desired thickness. At this time, the amount of reduction is not specified.
As also de~cribed in the aforementioned s~

1 Japanese Patent Publicatlon No. 432/1968, when heated to a temperature of 880C or above, the crystal system of titanium is transformed from close packed hexagonal lattice to body-centered cubic lattice and the crystal 5 grains grow. Moreover, titanium absorbs gases such as nitrogen, hydrogen and oxygen, and thereby the physical properties of titanium deteriorate. Accordingly, in this invention, hot rolling is desired to be carried out below 880C, preferably in the temperature range of 650 to ~70C.
It was confirmed that application of a heat treatment to the clad steel plate after rolling, if necessary, for improving t:he physical properties of the base metal did not cause large reduction in bonding strength and the clad steel plate had an excellent interface bond strength even after the heat treatment.
This heat treatment temperature is in the range of 540 to 870C. When the treatment is done below 540C, it does not contribute to the improvement of the characteristics of the base metal. When the treatment is conducted above 870C, the physical properties of titanium deteriorate as described above.
In the hot rolling of this invention, heating and rolling can be repeated several times. Also, process annealing can be applied to prevent the deterioration of the mechanical properties of the base steel~
Also, the clad steel plate 8-a can be produced _ 11 --1 by bonding the cladding metal l-B, the thin, three-layered clad steel plate 5~a and the base steel 3-~ to one another with rolling and ~inishing these three plates into a composite plate of a desired thickness. The clad steel plate 8-a may be also produced by firstly bonding the thin, three-layered clad steel plate 5-a and the base steel 3-B by the roll bonding process and then the cladding titanium l-B is bonded thereon by another bonding process.
In order to give a desired thickness to -the intermediate metal [2-A in Fig. 1, (b), 2-a in Fig. 1, (c), (d) and (e) and 2-a' in Fig. 1, ~f)] of the final product, the thickness of the original intermediate metal 2-A must be carefully decided by fully considering (1) the thicknesses of the titani~n plate l-A and the steel plate 3-A in Figure 1 (a), (2) the amount of reduction in rolling into the thin, three-layered clad steel plate 5-a of Figure 1, (c), and (3) the amount of reduction in rolling from Figure 1, (e) to Figure 1, (f).
The test conducted for the plate 8-a of Figure 1, ~f) in its "as rolled" condition revealed that the titanium cLad steel plate fully satisfied min. 14 kg/mm2 which is the specified value of shear strength of the titanium clad steel plate specified by JIS G
3603-1980. This titanium clad steel plate was subjected to heat treatment of 850C x 1 hr. and then tested for sheax strength. A shear strength which well satisfied the above JIS specification value was obtained. From the 1 results of tension test and bending test, the above titanium clad steel plate was pro-~ed to have an excellent bond strength and excellent ductility.
It was also confirmed that the present inven~
tion could provide thin or wide tltanium clad steel plate which cannot be provided by the conventional manufactur-ing process of explosive bonded titanium clad steel plate. Also, since the welding of clad steel plate is generally difficult, the fact that wide titanium clad steel plate having an excellent bond strength can be provided by the present invention method, is a significant matter.
Figure 2 shows another type of titanium clad steel plate manufactured by the present invention, in which an intermediate metal layer and a supplemental intermediate layer are comprised. In the figure, 2-C
is an intermediate metal correspondin~ to Claim 5 of this invention and is selected from tantalum, tantalum alloys, niobium and niobium alloys. In the figure, 4-C
is a supplemental intermediate layer selected from commercially pure copper, copper alloys, commercially pure nickel and nickel alloys, and is used to make the intermediate metal as thin as possible in the inal product. This supplemental intermediate layer must be a material which does not allow the formation of hard and brittle intermetallic compounds between the inter-mediate metal and the base metal.
In the above, the commercially pure copper is ~v~

l a copper plate of ~hich copper content is 99~ by welght or above, and copper alloys are the copper alloys containing at least 58% copper by weight. Also, the commercially pure nickel is a nickel plate of which nickel content is at least 99~0~ by weight, and nickel alloys are the nickel alloy plates containing at least 40.0%
nickel by weight.
This four-layered clad steel plate can be produced by bonding one layer successively on the base steel according to the conventional bonding process.
The four-layered titanium clad steel plate can also be produced by (l) previously bonding the intermediate metal 2-C and the supplemental intermedia-te layer 4-C
and then cold rolling or hot roll:Lng the bonded inter-mediate layer into a thin plate, (2~ bonding the thinplate to the base steel, and (3) inally bonding the cladding plate to the surface of the plate formed in ~2). Further, by hot rolliny this four-layered titanium clad steel, there can be produced thin or wide titanium clad steel plate which the conventional explosive bonding process could not provide. This four-layered titanium clad steel plate also can be subjected to heat treatment, after rolling, for improving the characteristics of the base metal. This four-layered titanium clad steel plate has an excellent bond strength and sufficient ductility, in as-rolled condition and after heat treatment.
Since the weldiny of clad steel plate is l generally difficult, the fact that large-sized titanium clad steel plate having an excellent bond strength can be provided by the present invention method, is signifi-cant.
Figure 3 shows a manufacturing process of four-layered titanium clad steel corresponding to Claim 7 of the present invention.
In Figure 3, (a), 2-D is an intermediate metal, and 4-D is a supplemental intermediate layer. These two intermediate metal plates are bonded together by a conventional bonding process such as the explosive bondin~ process or the di~fusion bonding process, into a clad plate 6-D as shown in Figure 3, (b).
By rolling this clad plate, a thin clad plate 6-d shown in Figure 3, (c) is obtained. In the figure, 2-d is the intermediate metal after rolling and 4-d is the supplemental intermediate layer after rolling. The rolling can be either of hot rolling or cold rolling, depending upon the material combination of the inter-mediate metal and the supplemental intermediate layer.After this rolling, the thin clad plate may be subjected to appropriate heat treatment for reducing the work hardening caused by the rolling.
The thin clad plate 6-d thus obtained i5 arranged between the cladding metal l-D and the base metal 3-D as shown in Figure 3, (d) so that the inter-mediate metal ~~d of the plate 6 d faces the cladding metal l-D and the supplemental intermediate layer 4-d o 35~
1 the plate 6-d faces the base metal 3-D, and these three pla-tes are bonded as shown ln Figure 3, (e). In the Figure, 7-D is the bonded clad steel plate. This bonding is carried out by a known bonding process of different metals, such as the explosive bonding process, the diffusion bondiny process or the roll bonding process.
In the explosive bonding process, the base metal 3-D and the thin clad plate 6~d are firstly bonded and then the cladding metal, 1-~ is bonded on the surface of intermediate metal 2-d. Alternatively, the three plates l-D, 6-d and 3-D are explosive bonded simulta-neously. The latter bonding is more efficient.
The diffusion bonding process can be performed either simultaneously or successively.
When the clad steel 7-D is converted to the clad steel plate 7-d of a desired thickness as shown in Figure 3, (f), the thickness of the clad steel 7-D is reduced to the thickness range from two thirds to one fiftieth by rolling, depending upon the rolling tempera-ture and -the reduction capacity of the rolling mill.
In Figure 3, (f), 6-d' is the thin clad plate after rolling, l-d is the cladding metal after rolling and 3-d is the base metal after rolling. The hot rolling can be conducted by repetition of heating and rolling several times. Further, a process annealing is also effective.
When the roll bonding process is used, at the time of rolling the clad steel 7-D, three plates 35~

1 namely the cladding metal l-D, the thin clad plate 6-d and the base metal 3-D can be bonded simultaneousl~
by rolling to finish into a plate of a desired thickness.
Alternatively, the thin clad plate 6-d prepared before-S hand is bonded to the base metal 3-D by the roll bonding pxocess, and then the cladding metal l-D is bonded thereon. Figure 4 shows a microstructure of the titanium clad plate with niobium intermediate layer obtained according to this invention.
As described above, there has been established, by the present invention, a method of manufacturing titanium clad steel plate having an excellent bond strength and excellent bending ability even after hot processing during its manufacturing process or even after heat treatment after the manufacturing process~
Examples of the present invention are explained hereinafter.

Example 1 (a) Commercially pure tantalum plate having 2 mm thickness, 100 mm width and 200 mm length was explosive bonded, as an intermediate metal, to a commercially available JIS G 3103 SB42 steel plate having 50 mm thickness, 100 mm width and 200 mm length. A commercially pure titanium plate having 5 mm thickness, 100 mm width and 200 mm length was explosive bonded on the surface of the intermediate metal. Thus, titanium clad steel was formed 1 Anticipating possible welding heat or excessive heat treatment, this titanium clad steel plate of this invention was subjected to heat treatment of 850C x l hr.
and air cooled. The titanium clad steel pla-te thus obtained was tested ~or shear of its interface. The result was shown in Table 1.
The result revealed that the titanium clad steel of this invention had an excellent bond strength.
(b) Three-layered titanium clad steel plate having the same combination and dimensions as shown in (a) was prepared by the explosive bonding process. This clad steel plate was heated for l hr. at 8S0C and immediately rolled into titanium clad steel plate of 11.4 mm thickness, 100 mm width and 1,000 mm length.
The result of shear test conducted for the interface of this titanium clad steel plate was shown in Table 1.
The result revealed that the titanium clacl steel plate of this invention had an excellent bond strength. Further, bending test was subjected to this titanium clad steel plate and the result indicated t:hat the titanium clad steel plate had an excellent bending ability.
(c) Titanium clad steel plate of 11.4 mm thickness, 100 mm width and 200 mm length, prepared in the same manner as in (b) was explosive bonded t,o commercially available JIS G 3103 SB42 steel plate having 50 mm thickness, 100 mm width and 200 mm leng-th. Then, on - 18 ~

t3~

1 its titanium surface was explosive bonded commercially pure titani~ plate haviny 5 mm thickness, 100 mm width and 200 r~m lenyth.
This titanium clad steel plate was heated for S l hr. at 850C and immediately rolled into titanium clad steel plate having 13.3 mm thickness, 100 mm width and l,000 mm length.
The shear strength of the interface of thls titanium clad steel plate was tested and the result was as shown in Table l. It was revealed that the titanium clad steel plate of this invention had an excellent bond strength.
(d) The titanium clad steel plate prepared in (c) was heated for l hr. at 850C and then air cooled. The shear strength of the interface of this titanium clad steel plate was tested and the result was as shown :in Table 1.
The result revealed that the titanium clad steel of this invention had an excellent bond strength.

~0 Example 2 Titanium clad steel plate were prepared in the same manners as in Example 1, except that commercially pure niokium plate was used in place of commercially pure tantalum plate used in Example l. The shear strength o the interface of each ~itanium clad steel plate was tested and their results were as shown in Table l.

1 These results showed that the tltanium clad steel plates of the present invention had excellent bond strengths.

Example 3 The titanium clad steel plate of Example L, (b) was prepared and cut into a size of 11.4 mm thickness, 100 mm width and 200 mm length. On the base stee:L side of this titanium clad steel plate was placed commercially available JIS G 3103 SB42 steel plate having 50 ~n thickness, 100 mm width and 200 mm length, and on the titanium side was placed commercially pure titanit~m having 5 mm thickness, 100 mm width and 200 mm length.
This assembly was diffusion bonded under vacuum ~:L0 4 Torr) at an elevated temperature of 700 to l,100C for at least 10 min. and at a pressure of at least 0.1 kg/mm2 for at least 10 min. This clad plate was heated for 1 hr. at 850C and immediately rolled into a titanium clad steel plate having 13.3 mm thickness, 100 mm w:Ld-th and 1,000 mm length.
The shear strength of the int~rface of this titanium clad steel plate was tested and its result was as shown in Table 1.
The result revealed that the titanium clad steel of this invention had an excellent bond strength.

Example 4 ~ 20 -85~

1 A commerciall~ ava lable cupro-nickel pla~e (JIS
H 3100 C7060P) having 2 mm -thickness, 100 mm width and 200 mm length was explosive bonded t-o commercially available JIS G 3103 SB42 steel pla-te ha~ing 50 ~n thickness, 100 mm width and 200 mm length. On the cupro-nickel plate side was explosive bonded commercially pure tantalum plate having 2 mm thickness, 100 mm width and 200 mm length. Further, on the surface of tantal~n was explosive bonded commercially pure titanium plate 1() having 6 mm thickness, 100 mm width and 200 mm length, and thus titanium clad steel plate was prepared. This titanium clad steel plate was heated for 1 hr. at 850C
and immediately rolled into titanium clad steel plate having 20 mm thickness, 100 mm width a~d 600 mm length.
lS This titanlum clad steel was again heated for 1 hr. at 850C and immediately rolled into titanium clad steel plate having 10 mm thickness, 100 mm width and 1,200 mm length.
The shear strength of the interface o~ this titanium clad steel plate was tested and its result was shown in Table 1.
The results indicated that the titanium clad steel plate of this invention had an excellent bond trength.

Example 5 Titanium clad steel having the same combination and same dimension as those o~ Example 4 was prepared 1 and heated for 1 hr. at 870~C and i~ediatel~ rolled into titanium clad steel plate having 20 mm thickness, 100 mm width and 600 mm length. The finishing tempera-ture in rolling was 750C.
The bond strength of this titanium clad steel plate was tested and its result was as shown in Table 1.
The result indicated that the titanium clad steel plate of this invention had an excellent bond strength.

Example 6 Using oxygen-free copper plate (JIS H 3100 C1020P) having 2 mm thickness in place of the cupro-nickel plate which is the supplemental intermediate metal in Example 4, there was prepared four-layered titanium clad steel pla-te having the same dimension as that of Example 4. This clad steel plate was heated for 1 hr.
at 800C and immediately rolled into a titanium clad steel plate having 20 mm thickness, 100 mm width and 600 mm length. The finishing temperature in rolling was 2(~ 520C.
This titanium clad steel plate was subjected to heat treatment of 1 hr. x 850C and then tested Eor i-ts bond strength. The result was as shown in Table 1.
The result revealed that the titanium clad 2S steel plate of this invention had an excellent bond strength.

35~
l Example 7 Commercially pure niobium plate and ox~qen-free copper plate (JIS H 3100 Cl020P) both bein~
commercially available were explosive bonded, and clad plate of (2-~12) mm thickness, lO0 mm width and 200 mm length was prepared. This clad plate was cold rolled into thin clad plate of (0.5~3.0) mm thickness, 200 mm width and 400 mm length. The copper side of this clad plate was explosive bonded on commercially available JIS G 3103 SB42 steel plate of 50 mm thickness, 200 mm width and 400 mm length, and further on the niobium side of this clad plate was explosive bonded commercially available titanium plate of 5 mm thickness, 200 mm width and 400 mm length. Thus, four-layered titanium clad steel plate having (5+0.5~3.0~50) mm thickness, 200 mm width and 400 mm length was obtained.
This titanium clad steel plate was heated for l hr. at 830C and hot-rolled into one fifth thick to obtained titanium clad steel plate having (l+0~l~0.6 ~lO)mm thickness~ 400 mm width and l,000 mm length.
The titanium clad steel plate thus prepared was tested for its bond strength. The result indicated that the clad steel plate had a shear strength of over 14 kg/mm2 which is the JIS specification value, even in as-rolled condition and also after heat treatment of 625C x l hr, ~ollowed by furnace cooling after rolling.

- 23 ~

s~

1 Example 8 Commercially pure niobium plate and comrnercially pure nickel plate both being commercially available were explosive bonded to obtain clad plate of (2~12) mm thickness, 100 mm width and 200 mm length. This clad plate was cut into two pieces each having (2~12) mm thick-ness, 100 mm width and 100 mm length. Niobium sides of both pieces were joined and they were made into one plate by peripherally welding. At that time, a release agent was coated between two adjacent niobium plates, and the air present between respective interfaces was replaced by an inert gas~ The plate was then heated for 1 hr. at 900C and subsequently rolled into a thickness of one fourth. By separatlng the plate obtained, two thin clad plates each having (0.5~3.0) mm thickness, 100 mm width and 400 mm lenyth were prepared. The nickel side of this thin clad plate was explosive bonded on commercially available JIS G 3103 SB42 steel plate of 50 ~ thickness, 100 mm width and 400 mm length, and further on the niobium side was explosive bonded commercially available titanium plate of 5 mm thickness, ]00 mm width and 400 mm length. Thus, four~layered titanium clad steel plate having (5~0.5~3.0-~50) mm thickness, 100 mm width and 400 mm length was obtained.
This titanium clad steel was heated for 1 hr.
at 830C and then rolled to a thickness of one fifth to obtain titanium clad steel plate of (1+0.1~0.6~10) mm thickness, 400 mm width and 500 mm length.

- 2~ -~ S$~

1 The titanium clad steel plate thus obtaLned was tested for its bond strength. The result indicated that the clad steel plake had an excellent bond strenyth of over 14 kg/mm2 which was the JIS specificatiorl value, even in as-rolled condition and a]so even after heat treatment of 625C x 1 hr. followed by furnace cooling after rolling.

Example 9 Commercially pure tantalum plate of 2 mm thickness~ 100 mm width and 100 mm length and oxygen-free copper plate (JIS H 3100 C1020P) of 10 mm thickness, 100 mm width and 100 mm length both being commercially available were diffusion bonded under vacuum (10 4 Torr) at 700 to l,100C and at a pressure of above 0.1 kg/mm for at least 10 min. This clad plate was cold rolled into a thickness of one fourth to obtain thin clad plate of (0.5~2.5) mm thickness, 100 mm width and 400 mm lenyth. The copper side of this thin clad plate was explosive bonded on commercially available JIS G 3106 SM41R steel plate of 50 mm thickness, 100 mm width and 400 mm length, and further on the tantalum side was diffusion bonded commercially available titanium pla~e of 5 mm thickness, 100 mm width and 400 ~n length under the same conditions as above. Thus, four-layered titanium clad steel plate of (5+0.5~2.5-~50) mm thick ness, 100 mm width and 400 mm length was obtained.
This titanium clad steel plate was heated for 35~

1 1 hr. at 830C and rolled into a thickness of one ~lfth to obtain titanium clad steel plate of (1+0.1+0.5~10) mm thickness, 400 mm width and 500 rnm lenyth.
The bond strength of this titaniurn clad steel plate was measured. The result revealed -that thls clad had an excellent bond strength of over 14 kg/mm2 which was the JIS specification value, even in as-rolled condition and also even after heat treatment of 625C x 1 hr. followed by furnace cooling after rolling.

Exarnple 10 By explosive bonding a commercially pure tantalum plate of 2 mm thickness, 100 rnm width and 100 r~
length and nickel plate of 10 mm thickness, 100 mm wldth and 100 m~ length both being commercially available, two clad plates each of t2~10) mm thickness, 100 mm width and 100 mm length were prepared. Tantalum sides of these two clad plates were joined and they were peripherally welded to be converted into one body. At that time, a release agent was coated between two adjacent tantalum plates, and the air present between respective interfaces was replaced by an inert gas. The assembly was heated for 1 hrO at 900C and then rolled into a thickness of one fourth to obtain a composite plate consisting of two thin clad plates each havlng (0.5~2.5) mm thickness, 100 mm width and 400 mm length.
Further, on both sides (nickel surfaces) of this ~ 26 ~

V8~

1 composite plate were placed two commercially available JIS
G 3103 SB42 steel plates each haviny 50 mm thickness, 100 mm width and 400 mm length, and after peripherally welding, this assembly was heated for 1 hr. at 900C and then rolled into a thickness of one half to carry out roll bonding between nickel and the steel plate. By removing the peripherally welding, two clad plates each having (0.25+1.75+253 mm thickness, 200 mm width and 400 mm length were obtained.
On the tantalum side of this clad plate was explosive bonded commercially available titanium plate of 2.5 mm thickness, 200 mm width and 400 mm length, and titanium clad steel plate of (2.5+0.25+1O75+25) mm thickness, 200 mm width and 400 mm length was obtained.
This titanium clad steel plate was heated for 1 hr. at 830C and then rolled into a thickness of two fifths to obtain titanium clad steel plate of (1+0.1~0.7 ~10) mm thickness, 400 mm width and 500 mm length.
The bond strength of this titanium clad steel plate was measured. The result showed that this plate had a shear strength of over 14 kg/mm2 which was the JIS
specification value even in as-rolled condition and also even after heat treatment of 625C x 1 hr. followed by furnace cooling after rolling.

Example 11 Between commercially available ti-tanium plate of 5 mm thickness, 100 mm width and 100 mm length and - 27 ~

3~6 1 commercially available JIS G 3103 SB42 steel plate of 50 mm thickness, 100 mm width and 100 mm length, there was interposed commercially pure niobium plate of commercial avallabilit~ having 1 mm thickness, 100 mm width and 100 mm length. This assembly was diffusion bonded under vacuum (10 4 Torr) at 850C and at a pressure of 0.5 kg/mm2 for 30 min~ to obtain titanium clad steel plate.
This titanium clad steel plate was ayain heated for 1 hr. at 830C and immediately rolled into a thickness of one f if th to obtain titanium clad steel plate of (1+0.2+10) mm thickness, 100 mm width and 500 mm length.
The bond strength of this titanium clad steel plate was measured. The result indicated that the plate had an excellent bond strength of over 14 kg/mm which was the JIS specification value.

Example 12 Two sets of each material used in Example 11 were prepared. They were arranged in the order of steel plate, niobium plate, titanium plate, titanium plate, niobium plate and steel plate. The assembly was fixed by periphery welding with a steel belt. At that time, a release agent was coated between two adjacent titanium plates, and the air present between respective inter-faces was replaced by an inert gas.
This material was heated ~or 1 hr. at 830C

l and immediately rolled into a thickness of one fifth, and two titanium clad steel plates each having (lfO.2flO~
mm thickness, lOO mm width and 500 mm length were preapred.
The bond strength of this titanium clad steel .~ plate was measured. The result showed that the clad steel plate had an excellent bond strength of over 14 kg/mm2 which was the JIS specification value.

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~ 32 -1 Example 13 Commercially available JIS G 3103 SB42 steel plate of 50 mm thickness, 500 mm width and 500 mm length, commercially pure niobium plate of 1.5 mm thickness, 500 mm width and 500 mm length, and commercially available titanium plate of 5 mm thickness, 500 mm width and 500 mm length were explosive bonded simultaneously to obtain three-layered titanium clad steel plate of (5+1.5+50) mm thickness, 500 mm width and 500 mm length.
This three-layered clad steel plate was heated at 850C for 1 hr. and immediately rolled into three-layered titanium clad steel plate of 11.3 mm thickness, 500 ~m width and 2,500 mm length.
From this three-layered titanium clad steel plate was cut the clad of 11.3 mm thickness, 500 mm width and 1,000 mm length. The base steel side of this clad plate was explosive bonded to commercially available JIS G
3103 SB42 steel plate of 150 mm thickness, 500 mm width and 1,000 mm length to obtain four-layered clad plate.
Further, on the titanium surface of this four-layered clad plate was explosive bonded commercially pure titanium plate of commercial availability having 10 mm thickness, 500 mm width and 1,000 mm length.
This five-layered clad steel was heated at 850C for 1 hr. and immediately rolled to obtain titanium clad steel plate of 34.2 mm of total thickness, 1,000 mm width and 2,500 mm length.
Mechanical test results of the above titanium ~ ~ ~4~3~

1 clad steel plate in as-rolled condition and after heat treatment of 850C x 1 hr. followed by air cooling ~7ere as shown in Table 2. Test items were in accordance with JIS G 3603 for titanium clad steel.
The test results showed that this clad steel was excellent in bond strength, ductility and bending ability, and well satisfied the specification values.
Microscopic observation for the cross section of the above titanium clad steel plate revealed that the intermediate metallic layer with a thickness of about 60 ~ did remain uniformly~ as shown in Figure 4.
Also, the titanium/titanium interface and the steel/steel interface both formed by explosive bonding after the first rolling underwent recrystallization and trans-formation at the time of the second hot rolling, andno traces of these interfaces were recognized.

Example 14 Commercially pure niobium plate of commercial availability having 1.5 mm thickness, 500 mm width and 500 mm length and commercially available oxygen-free copper plate (JIS H 3100 C1020P) of 14 mm thickness, 500 mm width and 500 mm length were explosive bonded.
This two-layered clad plate was cold rolled into clad plate of iO.3+2.8~ mm thickness, 500 mm width and 2,500 mm length.
From this two-layered clad plate was cut a clad plate of (0.3~2.8) mm thickness, 500 mm width 5~

1 and 1,000 mm lenyth. The copper side of this clad plate was explosive bonded on commercially available JIS ~ SB42 steel plate of 150 mm thickness, 500 mm width and 1,000 mm length and three-layered clad plate was obtained.
Further, on the niobium surface of this three-layered clad was explosive bonded commercially pure titanium plate of commercial availability having 10 mm thic~ness, 500 mm width and 1,000 mm length.
This four-layered clad steel plate was heated at 850C for 1 hr. and immediately rolled into titanium clad .steel plate of 32.6 mm thickness, 1,000 mm width and 2,500 mm length.
Mechanical test results of the above titanium clad steel plate in as-rolled condition and after heat t.reatment of 850C x 1 hr. followed by air cooling were as shown in Table 2. Test items were in accordance with JIS G 3603 for titanium clad steel plate.
The results showed that this titanium clad plate was excellent in bond strength, ductility and ~0 bending ability, and well satisfied the specification values.
Microscopic observation for the cross section o~ the above titanium clad steel revealed that the intermediate metallic layer and the supplemental intermediate layer did remain uniformly with thicknesses of about 60 ~ and about 560 ~, respectively.

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l where ~l ~ lower llmit of the speclfied value for the tensile strenyth of base plate, kgf/mm , ~2 = lower limit of the specified value for the tensile strength of the cladding plate, kgf/mm , tl = thickness of base plate, mm, t2 = thickness of -the cladding plate, mm.
Note (2~: Radius (R) for the face bend shall comply with the standard for the cladding plate. For the root bend, the radius (R) shall comply with the standard for the base plate (the outside of the bent part shall be free from cracks).
However, if the inside radius specified in the standard for the base plate is less than one time the overall thickness tT), it shall be as large as one timQ (the outside of the bent part shall be free from cracks).

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS.

1. A titanium clad steel plate selected from an unrolled plate and a hot rolled plate, in which a cladding metal layer selected from titanium and a titanium alloy is bonded to a base metal layer selected from a carbon steel and a low-alloy steel by an intermediate metal layer inter-posed between the cladding metal layer and the base metal layer; characterized in that the intermediate metal layer is selected from commercially pure niobium and tantalum.

2 . A titanium clad steel plate as claimed in claim 1, in which the intermediate metal layer is bonded to the base metal layer by an interposed supplemental inter-mediate metal layer selected from copper, a copper alloy, nickel and a nickel alloy.

3 . A titanium clad steel plate as claimed in claim 1 or 2, wherein the cladding metal layer consists of two layers selected from titanium and a titanium alloy .

4. A titanium clad steel plate as claimed in claim 1 or 2, wherein the base metal layer consists of two layers selected from carbon steel and a low-alloy steel.

5. A method for manufacturing titanium clad steel plate selected from an unrolled plate and a hot rolled plate; characterized in that a cladding metal plate selected from titanium and a titanium alloy, and a base metal plate selected from a carbon steel and a low-alloy steel are, respectively, bonded to opposite surfaces of an intermediate metal plate selected from commercially pure niobium and tantalum; and, when required, the clad steel plate is hot rolled.

6. A method as claimed in claim 5, in which the bonding process includes bonding the base metal plate and intermediate metal plate, respectively, to opposite sides of a supplemental intermediate metal plate selected from copper, a copper alloy, nickel and a nickel alloy.

7. A method as claimed in claim 6, in which the intermediate metal plate and the supplemental inter-mediate metal plate are bonded to each other and rolled prior to bonding with the cladding and base metal plates.

8. A method as claimed in claim 5 or 6, in which a further cladding metal plate is bonded to the cladding metal plate already bonded to the intermediate metal plate.

9. A method as claimed in claim 5 or 6, in which a further base metal plate is bonded to the base metal plate already bonded to the intermediate metal plate.

10. A method as claimed in claim 5 or 6, in which a further cladding metal plate and a further base metal plate are bonded to the cladding metal plate and the base metal plate, respectively, already bonded to the intermediate metal plate.

11. A method as claimed in claim 5 or 6, in which the bonding of the plates is conducted by a process selected from explosive bonding, roll bonding and diffusion bonding.